Such a single-tube vibration damper is known from DE-Pat. No. 3,434,877, where working chambers separated by the damper piston are in communication with a magnetically operable damper device arranged parallel with the damper piston. A compensation chamber provided with a gas filling under pressure is separated by a separator piston from the damping-fluid-filled working chamber. For the connection of the damper device with the working chambers, openings are provided in the cylinder, while a passage between the cylinder and the container is connected for the one part with the damper device and for another part with a working chamber. In the cylinder there is also situated a stop for the separator piston. The stop is formed by a wire ring arranged in a groove of the cylinder. In this design it is disadvantageous that in the fitting of the separator piston the latter must be pushed with the seal over the openings of the cylinder and over the cylinder groove serving for the reception of the wire stop ring. Thus in the assembly of the separator piston it is easily possible for damage to the sealing edge to take place, whereupon a satisfactory seal between the working chamber and the compensating chamber is no longer guaranteed. It is also disadvantageous that the stop ring, or the valve housing part protruding into the working cylinder and comprising the passage, considerably shorten the stroke of the vibration damper.
It is the problem of the present invention to produce a single-tube vibration damper of variable damping force which consists of simple components which are easy to produce, and permits problem-free fitting.